Here's our experience...
We took DD to WDW for the 1st time at age 4 and used the Combi Traveler Stroller, which folds like an umbrella stroller and weighs 11 lbs. The back partially collapses for naps and it has a hood for shade and a removable bar in front. Weight limit of 45 lbs. It was okay, but for what we spent, we should have purchased a "regular" stroller which would have had more room for her, a fully reclining back, better padding, and would have been of standard size. After she outgrew the Combi (height wise) we purchased a Graco QuikFold which is standard sized and folds with one hand. Much nicer for all of the above reasons. DD is now 6, (weighs about 47 lbs) and we are soon to make our 4th trip with her and the 3rd with the Graco stroller. The stroller was weighted for 45lbs, but we have seen no strain on the frame with her being slightly heavier. She is far more comfy in it than she would be in the strollers in the parks, and we can keep her dry during rain storms using a clear plastic weather sheild. We have also attached "Stroller Pockets" to the back to carry items in the parks, in addition to the basket underneath. No problems yet...just wish that there was a slightly larger version of this stroller for older kids (height & weight), as there are still times at this age that kids need the break from walking. Maybe I'll invent one and retire!!!!
IMHO, but I'd advise you to use a standard stroller with a collapsible back for your 3yo, as it is built to last longer than an umbrella type and s/he will be more comfortable all the way around. This way, you'll have it when the little one is older too! Taking your own strollers to WDW is the only way to go, if its feasible!
Have a great time!
Berta